1. Field of the Invention
Embodiments of the present invention generally relate to a micro electro-mechanical system (MEMS) device and a method for its fabrication.
2. Description of the Related Art
MEMS devices typically include a switching element that is movable between multiple positions, such as between a position in close contact with an electrode and a position spaced from the electrode. FIGS. 1A-1D are schematic cross-sectional views of a MEMS device 100 at various stages of fabrication according to the prior art. The MEMS device 100 includes a substrate 102 having a plurality of electrodes 104, 106, 108 embedded therein. A dielectric layer 110 is disposed over the substrate 102 and electrodes 104, 106, 108.
For MEMS that utilize an organic polymer as their sacrificial material, the adhesion of the first layer of the sacrificial material to underlying dielectrics is typically low. In order to fix the low adhesion issue, a silicon polymer is often added to the polymer system. However, the Si, upon removal of the organic sacrificial material, can leave residues behind that can be detrimental to the performance of the MEMS device. As an alternative to adding silicon to the sacrificial material, an independent adhesion promoter material can be used. The adhesion promoter is coated over the substrate, either through a spin-on or CVD type process, prior to the coating of the organic sacrificial material. If inorganic material is used as the sacrificial material, an adhesion promoter would not be utilized.
An adhesion promoter layer 112 is then deposited over the dielectric layer 110. The adhesion promoter layer 112 is used to adhere sacrificial material thereon. A first sacrificial material layer 116A is then deposited on the adhesion promoter layer 112. The first sacrificial material layer 116A is an organic sacrificial material comprising carbon, hydrogen, nitrogen and oxygen. The first sacrificial material layer 116A, the adhesion promoter layer 112 and the dielectric layer 110 are then patterned to expose the electrode 104. As shown in FIG. 1B, an electrical conductive material is then deposited and patterned to form the switching element 118. A second sacrificial material layer 116B is then deposited over the switching element 118. The second sacrificial material layer 116B and the first sacrificial material layer 116A are then patterned using standard semiconductor processing techniques. The cavity 114 is bound by a roof 120, walls 122 and the dielectric layer 110 as shown in FIG. 1C.
As shown in FIG. 1D, the first and second sacrificial material layers 116A, 116B as well as the adhesion promoter layer 112 are then removed to free the switching element 118 within the cavity 114 so that the switching element 118 may move from a position spaced from the electrode 106 to a position in close proximity to the electrode 106 (i.e., in contact with the dielectric layer 110) as shown by arrow “A”. The first and second sacrificial material layers 116A, 116B are removed by etching using an H2/O2 chemistry introduced through a release hole (not shown) formed in the roof 120 or in through a hole in the side of the cavity. Any silicon contained in the organic sacrificial material would not be etched and would thus remain in the cavity as residues 124. The residues 124 are believed to be remnants of the adhesion promoter layer 112 or silicon that may be present in the sacrificial material. Specifically, silicon present in the adhesion promoter layer 112 or within the sacrificial material may lead to nanoscopic silicon (i.e., silicon with a vacancy in the 1 s orbital), which is very prone to charging. The residues 124 can interfere with the MEMS device 100 performance by mechanically impeding the switching element 118 from moving into close proximity to the electrode 106. The residue can also alter the electrical switching behavior of the MEMS device 100 by storing charge within the silicon that results in a hysteresis loop narrowing, where the difference between the pull-in voltage applied to electrode 108 which causes the cantilever it be pulled down and that at which the cantilever releases back up, gets smaller.
Therefore, there is a need in the art for a MEMS device and a method for its manufacture in which residues do not interfere with device performance.